Procurement of a tissue sample from a living body is one most important step toward diagnosis of and management plans for a disease in a range of medical fields. Traditionally, both open surgical biopsy and core needle biopsy techniques have been available for tissue biopsy. Open surgical biopsy, however, requires anesthesia and a relatively large incision on skin yet discovers a benign lesion in many patients who end up with surgical scars. Compared to open surgical biopsy, core needle biopsy has been shown to minimize complication rates while achieving high rates of sensitivity and specificity of correct tissue diagnosis equivalent to those following the open surgical biopsy. Regarding techniques for core needle biopsy, image-guided needle biopsy techniques have been shown to be superior to freehand, unguided biopsy techniques in terms of diagnostic sensitivity.
Visual guidance using ultrasound images has been successfully used for inserting core biopsy needle into tissue, resulting in high rates of sensitivity of tissue diagnosis. For an example, sensitivity of a ultrasound guided core needle biopsy for women with a suspicious lesion in breast has been above 97%, compared favorably to 86% of a freehand biopsy technique. The majority of ultrasound guidance devices use a separate needle guidance device reversibly attachable to an ultrasound transducer head. An operator takes a look at ultrasound images of a target on a monitor of an ultrasonographic apparatus, and visually estimates an approximate angle that a core biopsy needle needs to be at in relation to the target. While holding the ultrasound transducer by one hand and monitoring ultrasound images, the operator then pushes in the core biopsy needle using the other hand.
One drawback of the visual guidance for needle insertion is that since it depends on an operator's subjective visual estimation of an angle and length of a biopsy needle, there is a steep learning curve to achieve enough dexterity and coordination of both hands for correct introduction of the biopsy needle. Not infrequently, several insertion attempts are made before finding a suitable path of the needle toward the target, which increases chances of shearing off important tissue structure such as lymphatics and blood vessels. Sometimes an assistant would be necessary, who would continuously scan a target area while an operator tries to introduce a needle to the target. The other difficulty of the visual ultrasound guidance comes from a need of hand-held positioning of a ultrasound transducer on a skin overlying the target, which requires a good hand-eye coordination and a well-trained hand holding steady the transducer throughout the procedure regardless of patient's movements like breathing. These technical difficulties could increase chances of bleeding and infection at a biopsy site, and increase chances of spillage of malignant cells or of infectious germs from the target to adjacent areas that are not involved by a cancer or an infection, respectively.
Increase in size and number of a core needle biopsy sample has been associated with increase in both the diagnostic sensitivity and specificity. Yet in practice, it has been limited by increase in rates of complications such as bleeding, internal tissue injury and infection. Unless a single introduction of a core needle procures multiple samples of a sufficient size, repetitive manual insertions of the needle under a visual guidance using ultrasonogram would increase chances of these complications. Vacuum assisted biopsy has been developed to procure multiple samples, yet it may not be applicable for internal organs such as lungs due to a concern of significant pneumothorax and bleeding. Organs having a high density of blood vessels in tissue such as liver or kidneys may not be suitable for vacuum assisted biopsy since there would be serious bleeding consequences from damaged blood vessels following the procedure.
These technical challenges may be overcome if visual ultrasound guidance provides an operator with objective numerical positioning data such as a length of a needle to reach a target from a skin and a trigonometric angle between a longitudinal axis of the needle and a horizontal axis of an ultrasound transducer visualizing the target. In addition to a visual information seen on a monitor, the data should increase chances of the needle reaching the target with less frequent attempts. Complications may also be reduced if the biopsy needle is guided in a positioning guidance device that is temporarily and firmly fixed to the skin overlying the target, which maintains position of the needle steady during the biopsy procedure.
Modern applications of visual positioning guidance for invasive procedures have evolved to combine ultrasound guidance with either CT (Computer-Tomogram)—or MRI (Magnetic Resonance Imaging) visualization, to increase sensitivity of the procedures. Yet concurrent visualization by both ultrasonogram and CT or MRI, which is regarded as most ideal for visualization, is hampered by a need to combine two imaging data in one display. Furthermore, MRI precludes concurrent use of metallic devices for ultrasonogram as the metallic components of ultrasonogram devices interfere with electromagnetic fields of the MRI.